With the widespread use of data communication networks in recent years, even in homes, so-called home networks are becoming used in each of which, by connecting, to a network, electric household devices, a computer, and peripheral devices, communication between devices can be established. In the home networks, data processing functions of network-connected devices are shared such that the devices communicate with one another, and the devices transmit and receive content to one another, whereby convenience and comfort are provided to a user. Accordingly, it is predicted that the home networks are increasingly becoming widespread.
As a protocol suitable in the configuration of such a home network, Universal Plug and Play (UPnP) is known. The Universal Plug and Play (UPnP) enables facilitated establishment of a network without requiring a complex operation, and enables network-connected devices to receive a service provided by each device without requiring a difficult operation and setting. In addition, UPnP has an advantage in that it is independent from an OS (operating system) in a device and it enables facilitated addition of devices.
In UPnP, connected devices perform mutual recognition by exchanging definition files based on the XML (eXtensible Markup Language). An outline of UPnP processing is as follows:
(1) addressing that acquires a self-device ID such as an IP address;
(2) discovering which searches for each device on the network, receives a response from the device, and acquires information, such as a device type and a function, included in the response; and
(3) service requesting that, based on the information acquired by the discovering, requests a service from the device.
Implementation of the above process enables provision and reception of a service using a network-connected device. A device connected to the network uses the addressing to acquire a device ID, uses the discovering to acquire information of a different network-connected device, and can request a service from the different device based on the acquired information.
For example, when a device on a client side plays back content, such as music data and image data, stored in a server, the client acquires information concerning content retained by the server. The server stores the content in a storage unit and also stores attribute information for the stored content. The attribute information includes, for example, titles of music and movie as content, an artist name, a date and time of recording, and, in addition, information concerning a compression form of data. These pieces of the attribute information are called metainformation.
For example, when the device on the client side needs to play back content, such as music data and image data, stored in the server, the device on the client side transmits, to the server, content information stored in the server, for example, a music or movie title, an artist name, data-compression-form information (such as ATRAC (adaptive transform acoustic coding) or MPEG (moving picture experts group)), and, in addition, a request to acquire various types of content attribute information such as copyright information, if needed.
In response to the request from the client, the server transmits, to the client, metadata (attribute information) concerning content retained by the server. Based on the metadata acquired from the server, the client displays content information on a display of the client device in accordance with a predetermined display program. For example, a playlist including artist names and titles, etc., are displayed on the display. Based on the displayed information, the user selects or confirms content to be played back, and transmits a content transmitting request to the server. After the server receives the content request from the client, transmission of content is performed from the server to the client, and the content is received and played back by the client.
The content stored as described above in the server can be searched for from a different network-connected device (client), and can be played back by specifying a particular piece of the content.
For example, when the client selects music content as what is to be played back, a content transmitting request including an identifier of the music content is transmitted, and the server acquires the specified content from a storage unit and transmits the acquired content to the client. The transmitted content is played back. In a typical form of transmitting and receiving content data of the above type, the transmission and reception are executed basically in units of one piece of content or a set of plural pieces of content.
However, a client user has a case in which a desired piece of music for listening cannot always be specified based on general content information such as a title and an artist. As for so-called music, there are many cases in which, by listening to a characteristic melody portion such as a “transitional” portion, a piece of music can be identified. In addition, there is a case in which the user wishes to listen to only a characteristic portion or only a user's favorite melody portion without playing back all music content. For example, there are many users who wish to perform content playback in which only impressive portions are extracted from plural pieces of music content and are consecutively played back.
Many current systems in each of which content is stored in a home server, or the like, and a client makes a content transmitting request to the home server by specifying the content, a server can perform only content-unit transmission, but cannot perform the above content delivery such as extracting only data of user's favorite portions from server-stored content and transmitting the data to the client.
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2001-142495) includes a description concerning a configuration in which index information is set as management information for music content and in which specific content-portion-region specifying information is set. However, although, in the configuration in this Patent Document 1, one content playback processor manages and uses index information, Patent Document 1 does not represent a server-client system, that is, a configuration in which content is stored in a server and the content is provided from the server to a client in response to a request from the client.
In a current server-client system, a content request from a client is made by specifying content-identification information, and content transmission from a server is executed based on the content-identification information from the client. Therefore, extraction and transmission, by the server, of data in response to a partial content request concerning only a user's favorite portion are not realized.